Tay-Sachs Disease (TSD) and Sandhoff Disease (SD) are closely-related lysosomal storage diseases resulting from deficient activity of the enzyme yS-N-acetlyhexosaminidase (Hex). Collectively categorized as 'GM2 gangliosidoses,'these inherited neurodegenerative diseases were first described in 1881 yet remain invariably fatal to date. Initial results with AAV gene therapy in a mouse model of GM2 gangliosidosis have been extremely encouraging, with mice treated by intracranial injection of vector living >3 times longer than untreated mice. The goal of this translational project is to ready the promising AAV vector system for human clinical trials by performing all necessary preclinical experiments in mouse and cat disease models (Specific Aims 1 and 2), preparing GMP-grade vector for GLP toxicity and biodistribution studies (Specific Aim 3) and obtaining approval for trial initiation from all necessary regulatory bodies (Specific Aim 4). This project will be conducted by members of the Tay-Sachs Gene Therapy Consortium (www.tsgtconsortium.com), a group of scientists with proven track record in gangliosidoses and gene therapy from 4 institutions: Mass. General Hospital, Univ. of Cambridge (UK), Boston College and Auburn Univ. Studies in GM2 mice will demonstrate first the bioequivalence of a new AAV vector formulation injected bilaterally into the thalamus and deep cerebellar nuclei, followed by long-term efficacy and safety studies out to 20 months of age. In GM2 cats, we will first test the stability of the therapeutic effect of the new AAV vector formulation injected bilaterally into the same structures at 4 weeks of age, and validate clinically relevant tools to assess therapy. Finally we will evaluate the long-term safety and efficacy of the AAV vector formulation in GM2 cats allowed to survive up to 2 years of age. Once this phase is completed, Genzyme Corporation will produce GMP-grade vectors for GLP toxicity and biodistribution studies at the Univ. of Florida Powell Gene Therapy Center. Regulatory approval will be obtained with the assistance of an experienced regulatory consultant in the final year of this project. The experience and methodology gained from this project will be available for immediate application to the >40 lysosomal storage diseases, most of which have brain involvemen